Fuel cells have become an increasingly viable source of power, with recent technical advances creating smaller, lighter, and more efficient systems. As these power source solutions become technically mature, they will provide novel solutions for field applications. One such application is the utilization of the fuel cell in conjunction with rechargeable batteries. For example, Frerking, et al, in U.S. Pat. Nos. 6,441,589, 6,624,616, and U.S. patent application Ser. No. 2004/0104705 (hereafter referred to as the Frerking patents), generally describe a portable system and method for recharging secondary batteries. The Frerking patents describe a portable power source (which may include a fuel cell), a battery holder and socket, and circuitry for recharging the battery which includes a supervisory circuit, and a DC-DC converter for maintaining the correct charge state of the battery. In each case the DC-DC converter output is directly coupled to the battery, and means are employed to measure the current during the charging process in order to control the DC-DC converter.
While the Frerking patents disclose a workable system, there are some shortcomings to the utility of such a system. First, in the fabrication of a portable power system, the utility of the device can be greatly increased by adding the capability of using the fuel cell source to supply external power beyond the limited role of recharging batteries. Further, as external loads often have power surge requirements, the batteries in the system could also be used to supply power when the load exceeds the capability of the fuel cell. The batteries could additionally be used to supply start-up power for the fuel cell and, if employed, a fuel processor.
Fuel cell systems which supply power to a load typically employ batteries for start-up and surge capability. However, as these batteries have a limited life span, they may eventually need replacing. This is particularly true for systems such as fuel cell scooters, which may discharge the batteries heavily on a daily basis. Since these batteries must be removed by disassembly of part of the fuel cell power system, a better means for accessing and replacing defective or aged batteries is needed.